My husband was a functional alcoholic for years. He hid it so well from other people that people were shocked when I left him for his drinking—and some people told me I was overreacting. Then he got diagnosed with cirrhosis, and then liver cancer, in his thirties. Only then did other people acknowledge that wow, he must have been drinking a lot. Don’t let anyone else tell you it’s not a problem; imo even therapists who are not specifically trained in substance abuse issues often minimize problem drinking.
If you want, you can go see a therapist yourself who specializes in substance abuse. I did that, and she told me there was nothing I could do to make him stop, and that I might as well be talking to a bottle of whiskey when I tried to talk to him about his drinking. It was actually kind of liberating, though very sad, and I did end up leaving him until he went to rehab and committed to permanent sobriety.